In semiconductor fabrication, a plasma etching process can be used to transfer a photoresist mask pattern of a portion of a circuit onto one or more materials (conductors or insulators) on a semiconductor wafer. In the plasma etching process, the plasma acts to etch away materials exposed in the open areas of the photoresist mask pattern, i.e., in the areas that are not protected by the photoresist mask. The etching reaction is accomplished by chemically active and electrically charged species (ions) present in the plasma. The plasma is generated from a reactant mixture within a plasma chamber. In some applications, an electric field can be used to accelerate ions present in the plasma towards the wafer, thereby providing directionality to the etching of materials from the wafer. When the etching process is completed, the photoresist mask material is removed from the wafer.
During the plasma etching process, the photoresist material can be eroded or altered by the etching chemistry and/or etching byproduct materials. Too much erosion of the photoresist material can cause distortion in the photoresist mask pattern and corresponding etching distortion in the wafer. Also, without proper control, the etching byproducts can reduce the size of the openings of the photoresist mask pattern, thereby preventing the etching constituents of the plasma from reaching the materials to be etched. Moreover, the above-identified issues become even more problematic in fabrication of advanced devices that have high aspect ratio features and very small dimensions. It is in this context that embodiments of the present invention arise.